U.S. patent number 9,181,878 [Application Number 13/330,326] was granted by the patent office on 2015-11-10 for operations support systems and methods for calculating and evaluating engine emissions.
This patent grant is currently assigned to HONEYWELL INTERNATIONAL INC.. The grantee listed for this patent is Richard Ling, Kevin Moeckly. Invention is credited to Richard Ling, Kevin Moeckly.
United States Patent |
9,181,878 |
Moeckly , et al. |
November 10, 2015 |
Operations support systems and methods for calculating and
evaluating engine emissions
Abstract
In accordance with an exemplary embodiment, an operations
support system for an engine is provided. A diagnostics unit is
configured to receive engine data from the engine and to generate
condition indicators based on the engine data using a thermodynamic
model, the thermodynamic model being based on component maps
associated with the engine. An emissions calculation unit is
coupled to the diagnostic unit and configured to calculate
emissions information for the engine based on the condition
indicators. A graphical user interface is coupled to the emissions
calculation unit and configured to display the emissions
information.
Inventors: |
Moeckly; Kevin (Chandler,
AZ), Ling; Richard (Phoenix, AZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
Moeckly; Kevin
Ling; Richard |
Chandler
Phoenix |
AZ
AZ |
US
US |
|
|
Assignee: |
HONEYWELL INTERNATIONAL INC.
(Morristown, NJ)
|
Family
ID: |
47471551 |
Appl.
No.: |
13/330,326 |
Filed: |
December 19, 2011 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130158832 A1 |
Jun 20, 2013 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02C
9/00 (20130101); F05D 2270/71 (20130101); F05D
2260/80 (20130101); Y02T 50/677 (20130101); F05D
2270/08 (20130101); F05B 2260/80 (20130101); Y02T
50/60 (20130101) |
Current International
Class: |
G01M
17/00 (20060101); F02C 9/00 (20060101) |
Field of
Search: |
;701/29.1,31.1,31.4,32.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Goericke, J. et al.: "Operations Support Systems and Methods with
Engine Diagnostics" filed with the USPTO on Dec. 23, 2008 and
assigned U.S. Appl. No. 12/342,562. cited by applicant .
Moeckly, K., et al.: "Operations Support Systems and Methods with
Power Assurance" filed with the USPTO on Dec. 23, 2008 and assigned
U.S. Appl. No. 12/342,633. cited by applicant .
Moeckly, K., et al.: "Operations Support Systems and Methods with
Power Management" filed with the USPTO on Dec. 23, 2008 and
assigned U.S. Appl. No. 12/342,581. cited by applicant.
|
Primary Examiner: Elchanti; Hussein A.
Attorney, Agent or Firm: Ingrassia Fisher & Lorenz,
P.C.
Claims
What is claimed is:
1. An operations support system for an engine, comprising: a
diagnostic engine model unit configured to receive engine data from
the engine and to generate diagnostics data based on the engine
data; an engine-specific model unit coupled to the diagnostic
engine model unit and configured to receive the diagnostics data
from the diagnostic engine model unit and to generate engine
diagnostic scalars using an engine-specific thermodynamic model,
the thermodynamic model being based on component maps associated
with the engine; an emissions calculation unit coupled to the
engine-specific model unit and configured to calculate emissions
information for the engine based on the engine diagnostic scalars;
and a graphical user interface coupled to the emissions calculation
unit and configured to display the emissions information.
2. The operations support system of claim 1, further comprising a
GPS unit coupled to the graphical user interface and configured to
provide a location of the engine to the graphical user
interface.
3. The operations support system of claim 2, wherein the graphical
user interface is configured to display the emissions information
as a function of the location.
4. The operations support system of claim 3, further comprising an
emissions limit unit coupled to the graphical user interface and
configured to provide emissions standards for the location to the
graphical user interface.
5. The operations support system of claim 4, wherein the graphical
user interface is configured to display the emissions information
as a function of the emissions standards and the location.
6. The operations support system of claim 1, further comprising an
emissions sensor coupled to the emissions calculations unit and
configured to provide emissions data to the emissions calculations
unit.
7. The operations support system of claim 6, wherein the emissions
calculations unit is configured to calibrate the calculation of the
emissions information.
8. The operations support system of claim 1, wherein the emissions
calculations unit is configured to calculate the emissions
information in real-time.
9. The operations support system of claim 1, wherein the emissions
calculations unit is configured to calculate the emissions
information based on engine temperature, engine air pressure,
engine air flow, and engine fuel flow.
10. The operations support system of claim 1, wherein the
engine-specific model unit is further configured to adjust the
engine-specific thermodynamic model based on the engine diagnostic
scalars.
Description
TECHNICAL FIELD
The subject invention relates to the operations support of gas
turbine engines, and more particularly, to operations support
systems and methods for calculating and evaluating engine
emissions.
BACKGROUND
It is desirable to determine the emissions associated with
operation of a gas turbine engine. Such emissions are currently
estimated based on information from the engine manufacturer,
typically estimated for a nominal engine condition and operation.
Alternatively, emissions may be estimated based on sampling from
emissions sensors at the exhaust system. Conventional emissions
estimations may not be sufficiently accurate. Real-time engine
emissions depend on numerous parameters, including fuel, operating
speed and other operating characteristics, and individual engine
characteristics. Conventional estimations may not capture all of
these parameters.
The operation of a gas turbine engine powered aircraft would be
significantly enhanced if the pilot could be provided with
real-time information concerning the engine emissions. For example,
knowing the emissions may enable operating changes to improve
emissions, provide health information about the engine, and/or
enable improved compliance with environmental regulations.
Accordingly, it is desirable to provide improved operations support
systems and methods that generate improved emissions information.
Furthermore, other desirable features and characteristics of the
present invention will become apparent from the subsequent detailed
description of the invention and the appended claims, taken in
conjunction with the accompanying drawings and this background of
the invention.
BRIEF SUMMARY
In accordance with an exemplary embodiment, an operations support
system for an engine is provided. A diagnostics unit is configured
to receive engine data from the engine and to generate condition
indicators based on the engine data using a thermodynamic model,
the thermodynamic model being based on component maps associated
with the engine. An emissions calculation unit is coupled to the
diagnostic unit and configured to calculate emissions information
for the engine based on the condition indicators. A graphical user
interface is coupled to the emissions calculation unit and
configured to display the emissions information.
In accordance with another exemplary embodiment, a method is
provided for supporting operations of an engine. The method
includes collecting engine data; generating condition indicators
from the engine data using a thermodynamic model based on component
maps associated with the engine; generating emissions information
of the engine from the condition indicators; and displaying the
emissions information on a graphical user display.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will hereinafter be described in conjunction
with the following drawing figures, wherein like numerals denote
like elements, and wherein:
FIG. 1 is a block diagram of an aircraft system in accordance with
an exemplary embodiment;
FIG. 2 is a block diagram of an operations support system for
supporting and sustaining operation of an engine in accordance with
an exemplary embodiment; and
FIG. 3 is a schematic representation of a visual display rendered
on a graphical user interface of the operations support system of
FIG. 2 in accordance with an exemplary embodiment.
DETAILED DESCRIPTION
The following detailed description is merely exemplary in nature
and is not intended to limit the invention or the application and
uses of the invention. Furthermore, there is no intention to be
bound by any theory presented in the preceding background or the
following detailed description.
Broadly, exemplary embodiments discussed herein relate to
operations support systems and methods. More specifically,
exemplary embodiments include an engine diagnostics unit that
receives engine data from an aircraft engine and generates engine
emissions information based on the engine data using a
thermodynamic model. The thermodynamic model may be based on
component maps and be modified based on scalars. The emissions
information may be used to modify engine operation and/or reduce
engine emissions.
FIG. 1 is a block diagram of an aircraft system 100 in accordance
with an exemplary embodiment. In general, the aircraft system 100
includes an engine system 110 and an operations support system 120.
The engine system 110 may include a gas turbine engine, such as an
engine for an aircraft. In one exemplary embodiment, the engine
system 110 can include compressors that supply compressed air to a
combustor. The compressed air can be mixed with fuel and ignited in
the combustor to produce combustion gases. The combustion gases are
directed to high pressure and low pressure turbines that extract
energy, for example, to provide horsepower. In general, the system
100 disclosed herein may be employed in conjunction with any gas
turbine engine configuration. In one exemplary embodiment, the
engine system 110 is a gas turbine engine for an aircraft, such as
a helicopter. As discussed in greater detail below, the operations
support system 120 may be used to support a single engine system
110 or a number of engines, such as for a fleet of aircraft.
The operations support system 120 generally supports and sustains
operation of an engine system 110. For example, the operations
support system 120 processes engine data from the engine system
110; provides information about the engine system 110 to the pilot,
maintenance crew, and other interested parties; and optionally,
controls operation of the engine system 110. As described below,
the operations support system 120 additionally provides information
about emissions, including real-time or current emissions
information and emissions predictions.
In general, the operations support system 120 is located on-board
the aircraft. However, any of the components of the operations
support system 120 may be alternatively located off-board the
aircraft or a combination of on-board and off-board the aircraft.
In one exemplary embodiment, the operations support system 120 may
be embedded on-board an aircraft within a Full Authority Digital
Engine Control (FADEC), an engine control unit (ECU), or a Health
and Usage Monitoring Systems (HUMS) unit.
FIG. 2 is a more detailed, block diagram of the operations support
system 120 of FIG. 1. As shown, the operations support system 120
includes a number of functional units or modules 210, 220, 230,
240, 250, 260, 270, 280, and 290. The units 210, 220, 230, 240,
250, 260, 270, 280, and 290 each contain or share processing
components necessary to accomplish the individual and collective
functions discussed in greater detail below. As some examples, the
processing components may include digital computers or
microprocessors with suitable logic circuitry, memory, software and
communication buses to store and process the models within the
units discussed below.
As described below, the operations support system 120 receives data
from various parts of the aircraft and such data may be generated
by the on-board the aircraft or received from external systems,
aircraft, or ground operations that are off-board the aircraft. In
particular, the operations support system 120 may receive aircraft
instrumentation data from, for example, the cockpit, pilot, or
other system and engine instrumentation data from the engine system
110 (FIG. 1). The operations support system 120 may further receive
emissions information from emissions sensors 252 located at or near
the engine exhaust and location information from a GPS unit
262.
In one exemplary embodiment, the operations support system 120
includes a diagnostic engine model unit 210 that receives the
aircraft instrumentation data and engine instrumentation data as
input parameters. As an example, the aircraft instrumentation data
and the engine instrumentation data may include any suitable type
of data related to the engine or aircraft, such as for example, one
or more of the following: engine operating hours; static pressure,
total pressure, and temperature at various positions within the
engine system 110 (FIG. 1), such as the inlet or outlet of the
compressors, combustor, and turbines; gas producer speed; engine
torque; engine torque sensor voltage; temperature at the oil
resistance bulb; and metered fuel flow. Other engine data can
include the calibrated airspeed of the aircraft, ambient
temperature, and ambient total pressure. In general, any and all
parameters available to systems 110 and 120 are available for use
by model unit 210. The diagnostic engine model unit 210 generally
evaluates the input parameters and generates diagnostic
indicators.
The diagnostic model of the diagnostic engine model unit 210
develops scalars for each engine major engine component. The
diagnostic scalars are collected, trended, and statistically and
otherwise evaluated to produce a broad range of scalars for each
component that, at this point, represents the true aspects of that
component. These components are usually but not limited to the
aerodynamic rotational components of the engine system 110 (FIG. 1)
that are in basic form represented by maps within the engine model.
In one exemplary embodiment, the diagnostic engine model unit 210
provides signal conditioning such as in-range and signal validity
checks, unit conversion, scaling, filter/sampling, and steady state
detection. The diagnostic engine model unit 210 provides the
diagnostic indicators to the data trending and storage unit 240, as
will be discussed in greater detail below.
The diagnostic indicators from the diagnostic engine model unit 210
are also provided to an engine-specific model unit 220. The
engine-specific model unit 220 includes high-fidelity mathematical
representation of the engine system 110 (FIG. 1) for steady state
engine diagnostics. This mathematic representation may be referred
to as an engine-specific model. The diagnostic indicators from the
diagnostic engine model unit 210 are processed through the
engine-specific model to produce diagnostic scalars (or condition
indicators/engine parameters), as discussed below. As noted above,
the diagnostic scalars are developed in the diagnostic engine
model. As the diagnostic scalars are applied to the engine-specific
model unit 220, which is a similar model to that of the diagnostic
engine model unit 210, without the diagnostic capability of the
model, the model becomes a model specific to the engine when
generating the diagnostic scalars. In other words, at this point
the model is an engine-specific model and represents only that
particular engine at that point in time.
Generally, the engine specific model is embedded in the operations
support system 120 to provide continuous engine monitoring for
health and/or other types of engine attributes. Engine diagnostics
are achieved through adaptation of specific component parameters as
diagnostic scalars within the diagnostic model to measured engine
states.
In one embodiment of the engine-specific model unit 220, scalars
are the difference between expected engine states and the actual
engine states. These differences could be a result, for example, of
engine-to-engine differences and/or erosion of engine components.
In one example, the scalars can represent the erosion of the
turbine blades. The scalars may be utilized as coefficients,
biases, and adders used to adjust the aero-thermodynamic
representation of the model. As one example, the scalars function
to scale engine component airflows and efficiencies to match the
measured data. This matching process is accomplished by executing
an adaptive algorithm that iteratively adjusts or adapts the
nominal engine component efficiencies using the scalars. As such,
the thermodynamic engine model accurately mirrors actual engine
performance over time, and the model is improved as an
engine-specific model.
The model of the engine-specific model unit 220 is complete over
the entire operating range of the engine system 110 (FIG. 1). The
model is true to the workings of the actual gas turbine engine
system 110 (FIG. 1), and the manifestations of component-level as
well as engine-level performance changes from what would be
considered a "nominal" engine are superior to empirical,
algorithm-based models. In contrast, the interaction of empirical,
algorithm-based models can easily become skewed or distorted from
"true" performance, yet this distortion is not inherently obvious
when analyzing model-produced results from such a system. A
component-level map-based aero-thermodynamic physics model is much
more robust and accurate over the lifespan of an engine and
produces higher fidelity representations of its components.
In summary, the engine-specific model unit 220 uses one or more
component-level, map-based aero-thermodynamic models to obtain
component-level map scalars that characterize a specific engine,
which in turn produces an engine-specific model that is a
high-fidelity representation of the engine itself. The
engine-specific model unit 220 provides the engine diagnostic
scalars to the data trending and storage unit 240, as will be
discussed in greater detail below. The engine-specific model unit
220 may be in contrast to an algorithm-based system that uses
mathematical equations to try to develop relationships between one
parameter and one or more parameters in the engine. These
conventional models may lose accuracy as the engine deviates from a
"nominal" state over time or into more extreme operation, away from
where the algorithms were developed. In contrast, the model of the
engine-specific model unit 220 represents the true aero-physical
relationships in the engine in the same way a map-based
component-specific model does. Because the component maps have
first been developed with high-fidelity design practices and tools,
then tested extensively in strictly-controlled "rigs" over the
complete operating range of the component, and subsequently
confirmed in the engine with multiple highly-instrumented, highly
controlled engine-level testing, the map-based components may offer
an advantageous representation of a gas turbine engine and the
associated engine performance.
The predictive unit 230 receives the engine diagnostic scalars from
the engine-specific model unit 220 and evaluates the scalars with a
thermodynamic model similar to that of the engine-specific model
unit 220 with the exception that the thermodynamic model of the
predictive unit 230 does not react to engine data. As such, the
predictive unit 230 may have a model similar to that of the
engine-specific model unit 220 except that the model is predictive.
In particular, the predictive unit 230 trends the component scalars
over and projects the diagnostic scalars from the present to a time
in the future to establish an engine-specific prediction model to
forecast engine performance under user-supplied conditions as
prognostic indicators. In "predictive" mode, the model is no longer
"engine-specific," but is a "future engine-specific" model. As
such, the model of the predictive unit 230 may then be used to
predict engine performance at a specific rating condition (e.g.,
inlet temperature, altitude, power, installation configuration, and
the like) to produce prognostic indicators. The predicted engine
performance from the predictive unit 230 is also provided to the
data trending and storage unit 240. The output that may be trended
includes engine output performance, such as temperatures, fuel
flow, speeds, and powers, as well as specific component
efficiencies, airflows, and pressure ratios.
The emissions calculation unit 250 receives emissions data from the
emissions sensors 252, engine diagnostic scalars from the
engine-specific model unit 220, and prognostic indicators from the
predictive model unit 230. In turn, the emissions calculation unit
250 calculates the real-time emissions of the engine system 110.
The embedded emissions calculations may be empirically established
to use the pertinent gas path parameters to accurately calculate
engine emissions. For example, the emissions calculations may use
proper gas properties, gas molecular constituents, gas temperatures
and pressures and flows, and fuel flows, temperatures, and
properties throughout the engine system. Accurate calculations of
emissions may use the temperatures, pressures, flows, and fuel
flows from the units 210, 220, and 230 discussed above. This model
may more easily lend itself to accurate emissions calculations
using such model-generated information. The coding for these
emissions calculations may be updated or modified if new
information becomes available.
As discussed above, the operations support system 120 also receives
emissions data from emissions sensors 252, which may or may not be
considered part of the operations support system. Emissions sensors
can include sensors that detect indications of NOX, CO, CO2,
particulates, and unburned hydrocarbons, for example, and are most
commonly used to sample the engine exhaust gas stream. The
emissions calculation unit 250 may also make use the emissions
sampling from the emissions sensors 252 in the emissions
calculations, to recalibrate emissions calculation routines of the
emissions calculation unit 250, to refine calculations, and/or as a
validity check against calculated emissions. Such calibration may
occur in flight or in a ground-based equipment setting, during
maintenance, or any other sort of bench testing equipment. In some
embodiments, the emissions sensors 252 may be omitted and the
calibration may be obtained by other mechanisms.
The emissions calculation unit 250 may also estimate the emissions
of future engine use, e.g., using the prognostic indicators from
the predictive unit 230. The emissions calculation unit 250
provides the real-time emissions and the predicted emissions to the
data trending and storage unit 240. For example, the emissions
information may be considered with aircraft avionics or other
positioning system to track emissions output over the actual flown
flight path. Although illustrated as a separate unit, in other
embodiments, the emissions calculation unit 250 may be integrated
with the engine-specific model unit 220.
The emissions information is also provided to an emissions limit
unit 260. The emissions limit unit 260 compares the predicted
and/or real-time emissions to the appropriate rules, laws, and
regulations (e.g., generally "standards") concerning such
emissions. In one exemplary embodiment, the emissions limit unit
260 may also receive a current or predicted location of the
aircraft from the GPS unit 262, which may or may not be considered
part of the operations support system 120. As such, the emissions
limit unit 260 may compare the predicted and/or real-time emissions
to location-specific standards to produce emissions compliance
information.
The emissions compliance information from the emissions limit unit
260 is provided to an engine control unit 270. The engine control
unit 270 may evaluate the emissions compliance information to
determine if engine operation may be modified to lower the
emissions and/or comply with applicable emissions standards. For
example, with information about current emissions, the control of
these emissions may be implemented using available
engine-controllable variables to alter the engine state while
meeting engine output requirements and/or adjusting engine output.
In one exemplary embodiment, operation modification may include
varying engine speed, variable geometry, engine bleed, fuel flow,
fuel choice, exhaust parameters, and/or environmental changes.
Additionally, as described below, the engine control unit 270 may
make these adjustments automatically and/or provide suggestions for
pilot intervention or choice in engine operating mode. In one
exemplary embodiment, the engine control unit 270 may alter one of
these variables of engine operation until the desired emissions
level was reached, while still maintaining overarching confines,
such as output power, generator frequencies, bleed flow, and the
like. The location from the GPS unit 262 may also be considered by
the engine control unit 270 in evaluating and/or implementing the
appropriate response.
The emissions information and emissions compliance information may
be provided to a graphical user interface (GUI) 290, for example,
located in the aircraft cockpit for consideration by the pilot. The
GUI 290 generally includes any suitable display device for
displaying the information described herein and an input device for
interacting with the operations support system 120. Such displays
may include any suitable type of display medium capable of visually
presenting multi-colored or monochrome flight information for a
pilot or other flight crew member can be provided, such as, for
example, various CRT and flat-panel display systems (e.g., CRT
displays, LCDs, OLED displays, plasma displays, projection
displays, HDDs, HUDs, etc.). The GUI 290 may form part of a Primary
Flight Display and/or Multi-Function Display Unit.
As noted above, the data trending and storage unit 240 may receive
data from a number of sources, including input parameters from the
engine (e.g., engine system 110), diagnostic indicators from the
diagnostic engine model unit 210, engine parameters from the
engine-specific model unit 220, prognostic indicators from the
predictive model unit 230, and emissions information from the
emissions calculations unit 250. The data trending and storage unit
240 provides binning and storing of this data, as well as
statistical analysis and trending for use in historical analysis or
emissions performance over time. As an example, aircraft location
from the GPS unit 262 may be used as a trendable parameter. Data
trending of the emissions calculations may be used to increase
confidence in these numbers.
As an historical unit, the system 120 provides evidence of not only
an emissions rate of the engine at any chosen time, but also as
evidence of cumulative emissions over a chosen segment of time,
such as time spent at a particular location (e.g., an airport).
With historical records of emissions, and trending versus time,
usage level, and location, projections may also be made as to
emissions levels in the future. In this way, an engine may be
designated for maintenance actions prior to violating emissions
regulations, or chosen for use in alternate applications. Trending
of data also provides the opportunity to remove certain data or
predictions if determined to be an anomalous. With an appropriate
database of past engine performance and emissions, any number of
projections or uses of this history may be made.
In one exemplary embodiment, statistical analysis of the data
collected and generated by the operations support system 120 in the
data trending and storage unit 240 may be considered by a
maintenance unit 280 to determine if the engine requires
maintenance. For example, such data may result in the ground crew
adjusting the maintenance schedule of the aircraft and/or taking
corrective action with respect to emissions issues.
FIG. 3 is a visual display 300 rendered on the GUI 290 in
accordance with an exemplary embodiment. The visual display 300 may
include any of the parameters, inputs and/or outputs discussed
above, including health indicators, engine input data, diagnostic
scalars, maintenance information, and the like. In this exemplary
embodiment, the visual display 300 includes emissions information
310. The emissions information 310 includes time on the horizontal
axis and a quantity (e.g, pounds of CO2) on the vertical axis. As
noted above, the emissions information 310 may be based on location
provided by the GPS unit 262 and standards from the emissions limit
unit 260. As shown, emissions are calculated over time, as
indicated by line 320. As noted above, emissions information may be
plotted according to the location of the aircraft and the
appropriate emissions standard, as indicated by lines 312, 314, and
316. In the example shown, emissions were estimated to be within
the appropriate standard in the initial segments of the trip when
the aircraft is flying in the US and international airspace.
However, when the aircraft enters the EU, the standards are more
strict, and the current emissions are higher than the appropriate
standard in this example. A warning 340 may be provided to the
pilot or user when the current emissions are greater than the
standard. In FIG. 3, the current time is indicated by line 318, and
the emissions information 310 further estimates the future
emissions (noted by dashed line 330) to provide an indication about
the future performance of the aircraft. As shown in FIG. 3, the
emissions may be expected to fall below the respective standard
316. In other embodiments, suggested or automatic engine control
modifications (e.g., provided by the engine control unit 270) are
displayed on the display 300. Examples of such messages include
"reduce fuel," "adjust speed," and/or "modify route."
As such, the operations support system 120 enables improved engine
operation by continuous display of emissions conditions to a pilot,
prevention of unintentional emissions, and enabling compliance or
reduction of emissions. This results in a reduction in pilot and
crew workload, a reduction in emissions, and improved situational
awareness.
As noted above, the operations support system 120 is discussed in
conjunction with an aircraft engine. However, other types of engine
applications may be provided. Applicable engine applications
include, but are not limited to, airplane propulsion (fan,
turbojet, turboshaft, turboprop), helicopter propulsion
(turboshaft), and aircraft auxiliary power units, ground power
unit, power generation sets, shipboard power systems, and
industrial gas turbines.
While at least one exemplary embodiment has been presented in the
foregoing detailed description of the invention, it should be
appreciated that a vast number of variations exist. It should also
be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended
claims.
* * * * *